Oscillation generation and control



Oct. 19, 1937. c. w. HANSELL OSCILLATIONY GENERATION AND CONTROL Filed Oct. 4, 1935 7 Sheets-Sheet 2 m. 19, m7. w. HANSELL 2,095,930

QSCILLATION GENERATION AND CONTROL Filed Oct. 4, 1933 I 7 Sheets-Sheet s fA A JE l l l l i l I I I I I 754 INVENTOR C. W. HANSELL Oct. 19, 1937. c. WQHANSELL 2,095,980

' QSCILLATION GENERATIONAND CONTROL I Filed Oct. 4, 1933 7 Sheets-Sheet 4 50 67625 ama D. C- POWE? 500362 I I NVENTOR C.W' HANSELL ATTORNEY 0a. 19, 19.37. c. WLHANSELL 2,095,980

OSCILLATION GENERATION AND CONTROL Filed Oct. 4, 1935 7 Sheets-Sheet 5 VVVVVV EL E 3 INVENTOR ATTORNEY c.w, NSELL Oct. 19,1937.

c. W.,HANSE L.L OSCILLATION GENERATION AND CONTROL Filed Opt. 4, 1955 7 Sheets-{Sheet '7 INVENTOR c. .H NSELL ATTORNEY Patented Oct. 1 9, 1937 UNITED STATES PATENT. OFFICE oscnnrrroiv GENERATION AND coN'rnoL Clarence W. Hansel], Port Jefferson, N. Y., asslgnor to Radio Corporation of America, a corpoi-ation of Delaware Application October 4, 1933, Serial n... 692,092

pair of spaced conductors having appreciable 7 length relative to the working wave-length and having uniformly distributed inductance and capacity. The conductors'moreover are preferably linear and arranged parallel to each other. As

, explained more fully in my 'patent, standing waves produced upon the conductors serve to lock the oscillations generated by the device or de-.

vices, asthe case might be, into step therewith, and as the standing waves are determined in frequency solely bythe linear dimension of the line, high frequencystability'is' obtained. My 2 present invention deals with a similar arrangement but'has-as its aim the provision of an improved line controlled system which is particularly applicable for short waves and which shall be simple and inexpensive in construction and highly efficient in operation.

For high efllciency in the operation of my present line controlled system and for economy in the construction thereof I prefer to make the line controlling circuit in the form of concentric tubes whose diameter ratio's have certain definite values to be given more fully hereinafter. Moreover.

an especially important purpose of my present invention is to provide an improved line construction for use with pushpull connected multielectrode devices. To that end my present invention contemplates a U-shaped tubular construction over the legs of which, and insulatingly arranged therefrom, are placed metallic cylinders. The U-shaped controlling line is made, preferably, to have an ,overall length of some 1 multiple of a half wavelength and for most practical purposes I prefer to make the overall dimension one-half wavelengthtaken at the desired operating frequency. However, if we consider the two sides of the u to be opposite sides of a two conductor or balanced transmission line then the length of each'side is made a quarter wave or multiples of a quarter wave. My present inventionalsotakeswithinitsviewtheprovision ofapproximately elliptical tubular lines forfret 33 Claims. (Cl. 250-36) quency control, the construction 'of which, as well as the more detailed construction of my U- shaped lines, is based upon principles more fully set forth hereinafter.-

While my improved line controlled system is simple in construction, operation and maintenance, it is not completely infallible and occa-. sionally permits of small drifts in frequency. -A further object of my present invention is, therefore, to provide means both automatic and manual to adjust the effective length of my line controlling system whereby the frequency of operation is adjusted to a. desired value.

For automaticfrequency control it has been proposed heretofore to beat a controllable fre-' quency source against a constant frequency source. The resultant. frequency differentiated beat ispassed through two filters in such a way that if the beat, and consequently the controllable frequency, is of correct value, no potential difference will arise across the filter circuits.

' However, if the beat shifts in frequency, the potential difference across the filters is utilized to vary the frequency of the controllable oscillator so that the oscillator is shifted in frequency in such a way as to produce the desired heat. This system, however, suffers from the disadvantage that it is liable to produce the correct beat frequency note when the controllable oscillator is either above or below the desired frequency by the 'same amount. Consequently, with such an arrangement, confusion is likely to ensue since an operator cannot readily tell, with such an arrangement, whether or not -he is,operating above or below his constant frequency comparing wave. Therefore, a further object of my present invention is to provide a frequency correcting and controlling system which shall have only one possible frequency of operation.

In carrying out. this angle of my present in- 'vention I have discovered that the beat be-.

tween waves of nearly the same frequency reversesin polarity or phase asthe waves are passed through zero beat. Thisreversal of phase of the beat between energies of nearly like frequency as they are'passed through zero beat is utilized to adjust the frequency of a controllable oscillator so as to bring it back in frequency to correspond to that of a highly constant frequency wave.

. accurate with-respect to frequency control and 1 While my present improved frequency controlanddescribed as correcting the frequency of a. line controlled transmitter, or oscillation generator, it should be clearly understood that it is not limited thereto but may be applied as well to other forms of generators such as crystal controlled generators or simple regenerative oscillation generators or even to generators of electrical current of industrial frequencies.

In connection with the frequency control of an oscillation generator it is to be noted that a certain amount of leeway is permissible and in fact it is desirable that an oscillation generator be not corrected in frequency for every slight change which may occur since this would tend to subject the correcting apparatus to incessant operation with its concomitant undue wear. A further feature of my improved frequency controlling system resides in the provision of an arrangement which does not become operative to exercise its frequency control until a drift in frequency of a predetermined amount has taken place.

Some other objects of my present invention are to provide improved systems for rendering oscillation generators less liable to variation in frequency due to changes in temperature and vi.- bration of their buildings or supports, to provide improved fiuid cooled short wave'systems, and to provide improved ways and means for varying the effective lengths of the line of line controlled oscillation generators. Other objects and advantages of my present invention will appear as the more detailed description is given by making special reference to the accompanying drawings wherein, generally,

Figures 1a and 1b are, respectively, the top plan view and the side elevation view of an improved resonant line frequency controlled short wave transmitter employing many features of my present invention;

Figure 2 is an expanded variation of Figures 1a and 1b giving in greater detail the electrical circuits therefor as well as indicating the manner in which automatic frequency comparison and control with astandard source may be obtained;

Figure 3 is a schematic circuit diagram of a circuit for frequency control whichfor its operation depends upon my novel teaching to the effect that as two oscillators are passed through zero beat, there is a reversal in phase of the resulting beat;

Figures 3a and 3b are alternative circuits which may be used in the system of Figure 3.

Figures 4 and 5 are alternative circuits which may be used in place of a portion of the circuit shown in Figure 3;

Figure 6 is a modification of my improved line frequency controlled transmitter especially adapted for shorter waves;

Figure 7 is a further modified form of line controlled transmitter for short waves incorporating therein a modulating system especially adaptedtherefor; and,

Figure 8 illustrates an arrangement for adjusting the effective electrical length of my frequency control line system.

Turning to Figures 1a and 1b, one form-of my improved line frequency control transmitter is seen to include a pushpull master oscillator stage MO mounted vertically above a final power amplifier stage PA in turn feeding energy through transmission lines TL to an antenna not shown but preferably of the type described by P. S. Carter in his United States Patent No. 1,974,387, granted September 18, 1934. The power amplifier PA is preferably of the water cooled pushpull type such as described by H. E. Hallborg in United States Patent No. 1,963,131, granted J une 19, 1934:.

resonantshaped pipe having two legs 2, 4, and a trough,

bent, curved or bottom portion I. The legs 2, 4 are within the outside pipes or tubes 6, 8. The inside transmission line 2, 4, I may be made entirely of copper or of a bent piece of iron pipe covered or plated with copper, silver, gold or other low resistance material. It may also be constructed of material having a very low temperature coefficient of linear expansion, such as iron-nickel alloy over which has been applied a coating of low resistance material. At extremely high frequencies where the line dimensions are relatively small other core materials such as fused quartz, pyrex glass, porcelain, etc., may be used as core materials in order to obtain a low overall temperature coefiicient of expansion. Additional adjustable tube sections I8, I2 may be inserted or telescoped into the free electrical ends I4, I6 of the transmission line or U-shaped member 2, 4, 'I. The tubes I0, I2, serve the purpose of adjusting the tubes to exact frequency as do also the metal disks I8, 20 placed over the telescoped pipes III, I2, the disks I8, 20 being preferably slidable over the tubes I0, I2. By suitably dimensioning the disks or condenser plates 20, I8, variations in length of the long line, due to changes in ambient temperature or due to temperature rise from radio frequency losses, will cause an accompanying movement of the disks or condenser plates which may be made to vary the capacity between.

' them and ground or the end of the box 36, so as to compensate for the changes in length of the long line and hence hold frequency constant. Because the open ends of the line and condenser plates I8, 20 fluctuate at high potentials, it is preferred that they be enclosed within a shielding box 38 which may be mounted as shown upon the outer metallic pipes 6, 8, or if desired may be carried by the line supporting pedestals 26, 28.

The inner conductors 2, 4, 'I of the line frequency control system is supported within the outer piping B, 8 and held rigidly in position by Isolantite or Mycalex" insulators 34. Also, the inside pipe 2, 4, I is preferably filled with sand, rosin, lead, concrete or other material to reduce its natural period of vibration and to absorb vibration so that the electrical resonant frequency of the system will be more nearly constant. The outer tubes 6, 8 are connected together and to ground by spacers, clamps or conductors 9.

The power amplifier unit includes, naturally, a metal casing which houses and shields the various elements therein as well as supports the shielded master oscillator MO. The power amplifier casing 22 may be loaded at its base with concrete, lead or sand if found desirable to further reduce tendency to vibration. Also, beneath the power amplifier casing 22 as well as beneath the pedestal supports 28, 28, which are preferably of metallic piping and filled with sand or concrete, there is placed vibration absorbing material 38, 32 such as rubber, wood fiber or felt. As a consequence any tendency of the building to vibrate will be first clamped by the vibration absorption material before being transferred in reduced form to the oscillator apparatus. Q

As already indicated, the electrical circuits for the system shown in Figures 1a and 1b is given In within the insulating boxer housing 36 a means for automatically controlling the frequency of the long line controlled transmitter so as to follow or correspond with a controlling frequency.

Turning in greater detail to Figure 2, the master oscillator comprises a pair of electron discharge devices 38, preferably of the water cooled variety, each having a plate or anode 42, a grid or control electrode 44, and a cathode or filament 46. Across the anodes of the vacuum tubes '38, 40, there is connected a parallel tunable circuit 48 consisting of an inductance coil 50 and a variable condenser 52. The circuit 48 acts as a rough frequency controlling circuit for controlling the fre-- quency ofoscillation of the pushpull connected.

electron discharge devices 38, 40. The line (which may be long) for frequency control is connected through conductors 53, 54 directly and conductively to the grids 44, and acts to accurately maintain the frequency of oscillation and hence the output of the master oscillator M0 at a desired constant operating frequency. The

action of the long line LLFC for frequency control and several alternative detail arrangements are explained more fully in my United States Patent No. 1,945,546, supra. Briefly, the action of the resonant line for frequency control may be explained by considering the line to be an exceedingly sharp resonant circuit which causes the oscillator to oscillate very constantly at its sharply resonant frequency. In another light it may be said that waves traveling down the line are reflected back so that standing waves on the line pull or.lock the oscillations generated into. step with the standing waves, and since the standing waves depend primarily upon the length of the line not give the zero phase difference, the line tends for their frequency it will at once be seen that the length of the line is the prime determining factorfor frequency control. From still another angle it can be said that the standing waves on the line consist of an ingoing wave and a reflected wave,

and the line tends to act so as'to maintain substantially'zero difference between the ingoing and reflected wave, and since any shift in frequencyaway from the frequency for which the line is a correct number of quarter wavelengths long will to react upon the system so as to establish the zero phase difference.

The filaments are supplied with heating potential from a source I02 supplying filament transformers 58, 60. In some cases I prefer to supply the two filament transformers 58, 60 from dif- 'ferent phases of a two phase power supply in order to balance out much of the disturbing effects of alternating heating current. High voltage plate supply is obtained from leads 62, '84, connected to a rectifier 68.

The neutralizing condensers 68, III cross-connecting the anodes and control electrodes of tubes 38, 40, are adjusted so as to cause sufllcient feedback for oscillation generation. Another feature of my present invention'resides in the adjustment of these condensers so that the phase of the voltage on the grids is in advance, or in other words,-

so that the grid voltage leads the plate voltage. This adjustment is obtained by making the capacity of the neutralizing condensers somewhat larger than that required to cause perfect neutralization. By virtue of this adjustment appreciably better power efllciency than when using lagging phase is obtained as, for example,.by setting the neutralizing condensers below the. neutralizing point. By

1 the 'use of over neutralization, I have found that there is an improvement in eificiency and this may beexplained by considering that the time of travel of electrons in the tubes tends to make the plate current and the voltage'lag behind the grid voltage. Bymaking the phase of the grid voltage lead, the effect of time of electrontravel is counterbalanced as a consequence of which more nearlyv optimum adjustments are obtained. This shift in phase due to time of electron travel is a minor factor in neutralized amplifiers because of the.

fact that the relative phase of the grid and anode voltage is not important. However, I have found that it becomes quite an appreciable factor in oscillation generators particularly of the water cooled type and particularly when used at the shorter wavelengths. v

It should also be noted that, in the line controlled-oscillator, the losses in the line constitute the greater part of the total load. If the oscillator were adjusted for oscillation by virtueof under neutralization the effective resistance in the grid circuit would give the grid voltage a phase shift in a lagging direction and this added to the phase shift due to time of electron travel might come to a considerable total. On the other hand, if

oscillation is obtained by over neutralization, the

line losses cause a shift in grid voltage phase in a leading direction so that the final resultant phase shift is the difference between that due to line losses plus time of electron travel. In cases where the plate circuit losses are predominant, as may be the case where the oscillator feeds energy directly to an antenna, it may be preferable insome cases to obtain oscillation by under neutralization in order to obtain optimum phase relations between anode and grid radio frequency voltages.

In any case I choose between over and under neutralization to obtain optimum efliciency and the choice is principally governed by the distribution of loading in the circuits.

Grid bias and modulating potentials maybesupplied through conductor I2 connected to a metallic slip ring I4 at the electrical center of. the long line 2, I, 4 which usually will be found at the mid point of the C-shaped portion I of the line 2, 1, 4. The grids may be connected to similar-adjustable.

slip'rings I6, I8 and all three rings I4, I6, I8 may I -be provided with set screws which may, if desired, be soldered or brazed into fixed position after final adjustments have been made. The point I6, I8 should be chosen a sufficient distance away from the electrical center I4 upon the longmost of the current will tend to fiow in the outermost surface of thetubi'ng. To further reduce losses the inner pipe or line 2, I, 4 maybe made of copper and plated with a material of lesser resistivity such as silver. In caseswhere con stancy of effective resistance is important a thin layer .of gold on the surface is desirable. Gold has somewhat .higher resistivity thansilver'. or copper but is more free from tarnishing and therefore more constant. Also untarnishedfgold surfaces may very well'have lessenergy loses than tarnished silver or copper surfaces. The

cost of gold plating is not prohibitive at extremely high frequencies where the length of line is small.

As illustrated, the legs of the frequency controlling line are transversely spaced and arranged parallel to each other. The outer pipes 6, 8 prevent undesired radiation from the frequency controlling lines and protect it from disturbance due to other nearby equipment.

The minimum length of line which it is preferred to use as a stabilizing resonant circuit is substantially one-quarter wavelength, but, for

pushpull use as illustrated in Figures 1 and 2, it is desirable and convenient to use a line whose total length is one-half of the wavelength of the desired operating frequency. The half wavelength is folded up upon itself as illustraed to form a U, which from one extreme end to the other is approximately one-quarter wavelength of the operating frequency. By making the line longer and in this particular case any number of half wavelengths long, its energy storage capacity is increased giving rise to increased stability as well as reducing temperature rise due to its own losses. The amount of energy which may be stored in a line is roughly proportional to its length, and the temperature increase for a given storage of energy is roughly inversely proportional to its length.

For most practical purposes I prefer to make the long line system one-half wavelength in length.

A further feature of my present invention resides in the dimensioning of the inner and outer conductors of the long'jline system. I prefer to make the ratio of the inside diameter of the outer tubing to the outside diameter of the inner tubing between 2.5 and and preferably of a value approximately 3.6. By making the ratio 3.6, I have found that standard sized pipes may be used with the accompanying advantage of having a minimum power factor. This, of course, is advantageous inasmuch as the smaller the power factor the less will be the losses in the line. I have found the characteristic impedance of a line having this ratio of diameters is '78 ohms regardless of the absolute value of the diameters.

For a minimum voltage gradient, assuming a given total voltage between the inner tubing 2, I, 4

and the outer piping '6, 8, I have found that the ratio of an inside diameter of outer piping and the outside diameter of the inner piping should be 2.72. v

In order to obtain a minimum voltage gradient for a given total stored or circulating energybetween. the outside surface of the inner tube or transmission line 2, I, 4, and the inner surface of the outer tubing orshielding '6, 8, I have found that the ratio of inside diameter of outer piping to outside'diameter of inner tubing should be 1.65.

For a maximum economy in the use of material the ratio of inside diameter of outer piping to outside diameter of inner piping, should be 4.68.

There are some general rules or laws applying to concentric conductor transmission lines which are of value to those interested in this application to design problems. Some of these laws are-1. The power factor of a line is proportional to the square root of the resistivityof the material used in it. 2. The power factor of a line is inversely proportional to the square root of the frequency. 3. The power factor is inversely proportional to the diameters of the conductors so long as the ratio of diameters is constant.

4. The maximum allowableenergystorage capacity of a concentric conductor line is proportional to the square of the diameters of the conductors so long as the ratio of diameters is constant.

For a system operating at a wavelength of meters and using solid copper inner and outer tubes for the long line frequency control system, the overall length of the inner conductor should be very close to 5 meters or 16.4 feet. Actually its length should be somewhat less than this because end effect and other factors always tend to give the line an effective length somewhat greater than this. Also, when using condenser plates such as 20, I8 to compensate for changes in tuning due to temperature rise of the inside pipe, these compensating plates are electrically equivalent to a small section of piping or tubing. These plates, therefore, should be taken into c0nside'ration when making up the U-shaped pipe for long line control.

For a system operating at 13,420 kilocycles or 22.35 meters it will be found satisfactory to utilize an outside pipe having an inside diameter of 20 inches and an inside pipe having an outside diameter of 5.56 inches. The total equivalent length of the whole U shouldbe very nearly a half wavelength. At the wavelength taken, namely, 22.35 meters, the length of the U should be very nearly 11.175 meters or approximately 36.6 feet. It will be found that the power factor of such a system will be approximately 0.012 percent.

With respect to the outer tubes or conductors 6, 8 they are preferably cross-connected by connectors 9 and grounded along their length by grounding connections 80, 82, 84, 86. If desired the pedestals 26, 28 may be made of metal to further assist in maintaining the outer concentric conductors at ground radio frequency potential". The outer conductors, furthermore, may be made of a single piece like the inner conductor or transmission line and U-shaped, suitable openings being provided so as to enable connections such as 53, 54 to be made with the inner conductors and to the grids 44 of tubes 38, 40. It is preferred, however, to use two lengths of tubing for the outer tubes 6, 8 each length of which as shown is transversely spaced relative to their length dimensions and mounted concentrically about the legs of the inner frequency controlling transmission line.

The transmission line structure including the inner and outer conductors may be placed within a, temperature controlled room or box (not shown) in which the temperature may be maintained constant. Or, the transmission line for frequency control may be placed within a container and kept at a very low temperature by the use of various refrigerating methods, care being taken to properly insulate the entire structure with heat insulating material such as asbestos, felt or wool, and further care being taken to prevent condensation of moisture upon the line. The latter may be effected by placing within the temperature controlling structure some hydroscopic material such as calcium chloride.

If desired I may also arrange to circulate cooling water through the inner line or a portion of it. In other cases I may bury the line in the ground in a vertical or horizontal position and depend upon the relatively constant ground temperature to assist in preventing frequency drift due to change in ambient temperature. In some cases I may also circulate air through the pipes by means of a blower or fan. In other cases I may make the outer pipes and end boxes air tight to keep out dust and moisture or I may use compressed air between the pipes to increase the flash over voltage limit.

For modulating the system shown in Figure 2.

the plate voltage may be varied by introducing modulating potentials into the plate' voltage lead 84 by meansof a transformer or the grid voltage may be modulated by similarly introducing modulating voltages in the grid biasing lead I2. A

convenient scheme for modulating the apparatus I or code signalling is illustrated and is described ore fully in my copending application Serial umber 672,529, filed May 24, 1933, Patent No. 2,060,988, Novemberr 17, 1936. As illustrated in Figure 2 the oscillator grid negative bias potential is obtained by passing the rectified grid current of the tubes through the common grid resistor 88.v The transmitter is keyed by imposing a higher negative potentialon the oscillator grids from the keying circuit which consists of a key or relay 98 applying and removing negative potential from source 92 to the grids 94 of, the parallel connected keying tubes 98. The two rectifier tubes 98, I88 by rectification action rectify voltages from source I82 for use as negative cut-off bias for the two oscillator tubes 48, 38. Reactor I84 and condenser I88 act to smooth the rectified keying voltages. v

When key 98 is down and applies negative potential to the. grids 94 of the keying tubes 96, tubes 96 are biased to cut-off. Consequently, the bias rectifier 98, I88 is rendered inoperative so that no negative potential is applied to the grids 44 of the radio frequency oscillator tubes 38, 48. When the key 98 is up the grids 94 of tubes 98 assume filament potential as a consequence of which the tubes 96 become conductive allowing current flow from rectifiers '98, I88 to flow through resistor 88 as a result of which conductor 12 impresses a high negative bias upon the grids 44' of the radio frequency oscillation generator such'that oscillation ceases. In passing it may be noted that the resistance 88 is common to both the oscillator and the keyingcircuit. Condenser I88 is the radio frequency by-passing condenser and the resistor I I8 is provided to assist resistor 88 in establishing a grid bias for the grids 44 under oscillating conditions in tubes 38, 48. The

resistor I I8 is not essential to the operation of the system but is preferred, in some cases, since it assists in preventing spurious oscillations.

As the long line frequency controlled oscillators such as shown in Figure 2 are often placed out in the field with inexperienced help or placed in inaccessible places, and since for some reason or another'there may be a slight drift in frequency, I have provided means as shown in Figure 2 for automatically correcting the frequency of' the transmitter system so as to correspond with and closely follow some master controlling frequency such as may be generated by a .carefully controlled piezo-electric crystal controlled oscillator,

extension tubes I8, I2, the capacity between the ends of line or between each end and ground is increased or decreased thereby decreasing or increasing the frequency of operation. .The motor I I4 is operated by means of an electromechanical relay system H6 operating a switch H8 applying reversing potentials through leads I28 to the motor II4. v

For operating a reversing switch such as II8 to vary some controlling means so that a locally enerated frequency may correspond with some controlling frequency, methods have previously been devised for detecting relative variations I in frequency which have included the use of beats controlled, any shift in the frequency of the beat energy, which is passed through filters in such 10 a way that change 'in frequency causes energy to pass through one filter or another depending upon the direction-inwhich the frequency is changed, will give a resultant current across both filters which may be used for frequency correction pur- 15 poses. When operating such that the correct beat frequencies are obtained the output, of both filters are identical and hence there is no frequency correcting current.

However, the beat system has two operating 20 points since the correct operating beat may be obtained when the frequency of the locally generated wave corresponds with the correct beat used to operate the relay switch and motor mechanism H8, H8, I28, H4 .of Figure 2, I have provided an arrangement which has only a single. operating point and which will be incapable of In other words, the-beat system has 25' have illustrated in Figure 3 and which may be giving false indications incidental to the use of 35 the heretofore known beat system. Moreover, the arrangement shown in Figure 3 has the added advantage that it will be less subject to difficulties from audio harmonics which also tend to influence the operation of the beat system known to 4 the prior art. And in addition the circuit arrangements described in Figure 3 have the added advantage of being simpler and consequently less expensive due mainly to the elimination of the, heretofore required audiofrequency filters.

Turning in greater detail to Figure 3, which by the way is not limited in its application to an arrangement such as described in Figure 2, but

may be used for example to maintainconstant the heterodyne oscillator of a receiver or in gen- '5 eral make any local source correspond to some frequency controlling source, I have provided a consta t frequency source I22 which may be a Y piezoectric crystal controlled, and incidentally,

temperature controlled oscillation generator so 55 designed as to be substantially constant infrequency. Since large power output is not essential the oscillator I22 may be relatively small and consequently inexpensive. The output from the crystal controlled source I22 is fed through two 0 separate circuits I24, I28, to the input electrodes of two vacuum tube power detectors or rectifiers I38, I32. In one of the circuits I24, I26,.and as illustrated, in circuit I28, there is provided a phase shifter I34 which may be a tuned circuit, a 5

radio goniometer or an artificial transmission line. Obviously the constant frequency s'ource I22 may include frequency multipliers so that the output frequency corresponds in frequency to the frequency at which it is desired that the generator 70 I35 of controllable frequency be operated.

Rather than use a phase shifter the two" circuits I24, I28 may be tuned by condensers I38,

I48 in which case the phase shift may be obtained by simply adjusting one circuit above and the 7 I42, I44 of the detectors differ by from 30 to 90 degrees. I may also shift the phases by means of reactance and resistance circuits.

The detectors I30, I32, while shown to be of the three electrode type may be of the diode or four or five electrode types and, in fact, may be replaced by other forms of detector such as, the copper oxide type.

To the detector input circuits I42, I44, there is also supplied from coils I46, I48 connected, to the controllable source I energy from the controllable generator. The detectors I30, I32, therefore, produce in the low frequency transformers I50, I52, beats between energy fromthe constant frequency source I22 and-the source I35 to be controlled. It is to be noted that source I35 is to be operated at'substantially the same frequency as that of the output of the constant fre quency controlling source I22.

The beat frequency output of the two detectors I30, I32, will have a phase relation corresponding to the difference in phase between the currents in the two radio frequency circuits which couple source I22 with the inputs to the two detectors I30, I32. If, for example, condensers I38, I are set to give a. phase difference of 60 degrees between inputs from source I22 to the two detectors then, in the outputs of the two detectors will appear beat frequency energy with a frequency equal tothe difference between the frequencies of sources I22 and I35 and having a phase difference of 60 degrees.

The detectors, while shown of the bias type, are preferably in practice made to have grid leak resistors and condensers so as to eliminate the necessity of the grid biasing source. The outputs of the detectors, namely, the energies appearing in the secondaries of transformers I50, I52, are applied to the input or grid filament circuits of two vacuum tubes I54, I56 having a common output circuit including the electromagnetically operated relay system II6, I I8.

When the generator I35 of controllable fre-' quency is operating at exactly the output frequency of source I22, the beats appearing in transformers I50, I52 will be'of zero frequency and double the frequency of either of the sources I22, I35. The double frequency, however, will be shunted around the transformers I50, I52 by the action of by-passing condensers I58, I60 and the switch member I I8 will not be moved in either direction. However, with a shift in frequency of I35 away from the output frequency of controlling source I22 the direct plate currents of the two vacuum tubes I56, I54 will be unequal due to the phase relations existing between theirgrid voltages and thus any inequality in the plate currents is utilized to operate the relay system II6,

II 8 which in turn may operate an alarm, or (as shown in Figure 2), operate a reversible motor for automatically correcting the frequency of the controllable source. The principle upon which the system of Figure 3 operates may briefly be summarized by stating that as the generator I35 passes through zero beat, the phase relationship of the resultant beat frequency energies appear- .ing in transformers I52, I50, reverses or, shifts quently, the grid of I54 is the first to swing positween the two tubes is 60 degrees.

leading phase, will have an effective bias potenthe beat frequency increases, the variations in bined frequencies pass through zero beat, is utilized to cause the system to return to zero beat condition and hence substantially identical frequency of operation of the controllable source with the controlling constant frequency source. 5

To understand the operation of the device shown in the figure, it should again be noted that the polarity of the beat frequency outputs from the two detectors is reversed as the transmitter frequency I35 is varied through zero beat with respect to the output of the crystal unit. Consequently, if the transmitter frequency is above the crystal frequency, one of the vacuum tubes, say I56 will have its grid swung positive in advance of tube I54 by an amount of time-corresponding to the beat frequency and the phase relation between the two grid voltages. If the transmitter frequency is below the crystal frequency by a like amount, the polarities are reversed and, consetive instead of the grid of vacuum tube I56.

Under these conditions it is only necessary to provide some method for making the direct plate current of one vacuum. tube greater than that of the. other in accordance with the phase relations between their grid voltages. One method of doing this involves the use of a condenser and resistance such as are shown at I62. Assume thatthe time constant of condenser and resistance I 62 is such that beginning at, say 100 cycles, the condenser begins to cause an appreciable smoothing outof the voltage variations across the resistance. .Then the vacuum tube whose grid first swings positive will have grid rectification which will charge up the condenser and cause a negative potential to exist on the other tube at the time when it swings most positive. Assume, for example, that the phase relations be- Then if the excitation to I56 is leading in phase, I56 willhave its grid potential positive once each cycle and I54 will follow at 60 degrees or one-sixth of a. cycle later. It will then be five-sixths of a cycle before I56 again swings positive. Consequently, the time for the condenser to lose its charge after I56 swings positive, isonly one-fifth as great as the time allowed for the charge to leak off in the time which elapses between I 54 and I56 swing ing positive. Consequently, tube I56 with its tial less than I54 and its plate current will consequently be greater than I54. If the polarities are reversed, I54 will be closely followed by I56 and there will be a relatively long time interval between positive peaks on I56 and I54 and, consequently, I54 will have a lower average bias, potential and its plate current will predominate.

Thus it may be seen that the time discharge rate of condenser and resistance I62 in combination with the phase relations in the excitation between the two vacuum tubes, will give a differential plate current variation as the transmitter frequency is varied through zero beat with respect to the output of the crystal oscillator. If

potential across circuit I62 will tend to be smoothed out and reduced to smaller and smaller values. This would result in the differential variation decreasing at relatively high audio frequencies and would limit the maximum operating band in which the tube currents could be used to indicate in which direction the transmitter had varied. The'frequency band may be increased by using a second resistance condenser circuit I66, connected in the plate circuit of the tubes. This 7 circuit may beadjusted to have a different time constant than that of circuit I62. In this case it may be assumed that the condenser of circuit I66 begins to cause a lag in the potential across the resistance -'at a point where the audio frequency is so high that circuit I62 is beginning to lose its effect; In other words, the operating ranges of time constant circuits and the transformer action action of the two tubes still further. ample, assume that the excitation to tube I56 circuits I62 and I66 are made to overlap in such a way as to obtain almost twice as large an/operating band as could be obtained with one circuit.

To still further widen the operating band, additional circuits of still different time constants such as I66, I10, may be serially connected in the common grid lead I12 and also in the platecircult, in series with. I66, if desired. In addition to the time constant circuits I62, I66 etc., the relay coil II6 may have considerable'inductance and operate as an audio frequency auto transformer or, if expedient, two windings of a transformer may be connected in series with the two sides of the relay in such a way that their magnetic fields are adding in a common core. This transformer action may be utilized to extend the differential For exleads I54 by 60 degrees. Then when tube I56 has its current increasing it will make the plate of I54 more positive but this will not cause a current to flow in I54 because at this time its grid potential is still negative. However, at the time when the current in I56 is decreasing this will' make the plate potential of tube I54 lower at a time when its grid is positive and the plate current will consequently be less in I54 than it otherwise would have been. Thus, the action of the of the relay all tend to cause the tube with the leading phase to have a higher'plate current than the other tube. If the transmitter frequency moves through zero beat in such a way as to make the excitation to I54 lead that of I56, then I54 will have a predominating plate current and the relay will be reversed.

' tubes, and further a bias source may be connected In order that the operator may have an indicator to show which way the frequency is varying before the relay has operated, a double range d-c voltmeter I14 may be connected across the relay coil. The direction of reading in this meter willthen show whether the transmitter frequency is above or below the correct value. If preferred, two separat 0 meters I16, I16 may be used in series wit he plate circuits of the two vacuum controlling arrangement illustrated in Figure 3' .it is, to be remembered that source I35 is to be controlled or operated within quite narrow limits,

,at the same frequency as'the frequency of oscillation of sou rce'l22. When both sources, namely I 22 and I35, are of the same frequency, there will be zero outputfrom the detectors I30, I32 as a result of which there is either no current or uni-.

form current flow through the tubes I56, I54 and the tbngue I I8 is not moved to either direction. Should generator I35 drift in frequency above that of source I22 therelative phases of the resultant beats from the two detectors will differ in one direction and should the generator I35 fall below in frequency with respect to the frequency of source I22, the phase of the resultant beats will differ in the opposite direction. That is, the

polarity of the beat frequency output from the two detectors I30, I32 is reversed as the source mon grid circuit for both tubes I56, I54. A time later, when tube I54 is operated there will have been impressed from the previous operation of tube I56 a negative potential on the grid of tube I54 as. a result of which with a continuation of the condition just assumed, the mean current flow through tube I56 will be greater than that through tube I54. In other words, that tube of the two tubes I 56,'I 54 which has the beat ap= plied in leading phase, tends to rob the other tube of current causing the tube experiencing "the leading phase excitation to draw a greater aver age current than the other tube. As shown" in Figure 3 the greater current is caused to operate a relay tongue in one direction or another-in 'turn causing a reversible motor to turn in one way or another and preferably in such a way asto cause the generator of controllable frequency tube adjusted so as to return to a frequency corresponding exactly with thefrequency cf the constant frequency source I22 and so that there is substantially zero beat between the controllable source I35 and the controlling source I22 again.

It will, of course, be possible to make many modifications in the detail arrangements of Figure 3for' carrying out this important aspect of my present invention. For example, the detector tubes may be of the grid leak type instead of the power type as shown. The output transformer for the detectors may be made of. relatively low exciting reactance, if desired, so that the audio frequency outputs to the first detector tubes are kept small until the transmitter frequency has varied more than a predetermined amount. For example, it may be desirable not to make any correction of the transmitter frequency unless it varies more than 250 cycles from parent that for the sake of. simplicityI have omitted the circuits for supplying filament heat- 0 ing energy. In practice, the filament heating might be from either a (1-0 or ac source and probably an m-c source would be used.

In practice I may combine the functions of I tubes I54, I56 with those of I30, I32 by applying the' condenser-resistance circuits I10, I68, I62, I66 and the relay coil I I6 to the grid bias and anode supply circuits of the detector tubes I30, I32. I have shown two separate pairs 'of tubes in Figure 3, for carrying out the functions of radio frequency detection and audio phase detection, in order to make the scheme easier to comprehend.

Obviously combining both functions in one pair of tubes will result in economy in equipment.

In place of two ordinary vacuum tubes such as I54 and I56, we might use vapor electric devices sold under the name of "'I'hyratrons or Grid Glow Tubes. These devices, which are struck into actionby grid excitation, but are extinguished only by reduction in plate voltage, are supplied with anode energy from a 60 cycle source with circuits such that the first tube to have its grid swung positive would become a short circuit for a half cycle of the 60 cycle energy and would short circuit the anode supply of the lagging tube to prevent it breaking down at all. In this case, the leading tube would carry rectified current and the lagging tube would remain an open circuit. Such a circuit has been ;;illustrated in Figure 3a which shows Thyratron" or ,grid glow tube circuits suitable for carrying out; thesame functions as tubes I54, I56 and their associated circuits in Figure 3. It should be noted that the circuits of Figure 3a are not limited in application to radio equipment but may also be used in audio or power equipment to indicate phase relations. For example, in power generating stations the tube circuits may be utilized in performing most of the functlons ordinarily performed by synchroscopes, even including the closing of circuit breakers to connect generators to the power system at the instant the generators have the same phase as the power system. A disadvantage, though not a very important one, of using vapor devices is that it would not be convenient to provide a voltmeter or other instruments to indicate to an operator the drift in frequency before the relay operated so that he might quickly make manual adjustments to prevent operation of the alarm or automatic correcting device.

In greater detail concerning Figure 3A, the beats to be compared are fed as before to the grids of vapor electric devices T1, T1. Thetubes T1, T2 are biased by the C battery arrangement shown which may be replaced by a source of rectified a-c, such as a potentiometer resistance across a copper oxide rectifier. Whichever tube is struck by leading phase grid potentials will cause an are or glow discharge through either tube T1 or T2 and the voltage drop produced in the common plate resistance R will prevent current flow through the other tube as its grid swings positive a short time later. It is to be noted that in the system of Figure 3A, a--c potentials are used for energizing the plate electrodes. This is done in order to periodically break the plate current through the tubes, otherwise,' with dc on the plates, and .with one tube drawing current, that tube would no longer allow of desired operation as it would continue to keep the other tube extinguished even though, later on, leading voltages were applied to the other tube. Still another very useful and practical circuit to detect phase changes is illustrated in Figure 3b. In Figure 3b, I have shown a tripping circuit, described by James L. Finch in his U. S. Patent 1,844,950 which consists of a pair of multielectrode vacuum tubes TIi, T'I'z, inter-linked by means of resistance coupling circuitsR l, R5, R6, R1, in such a way that if either tube predominates in carrying plate current it will cause the other tube to cut off and its own current to be a maximum. If this condition of current through a single tube is disturbed by momentarily forcing current to flow in the tube which had out 01! and at the same time decreasing the flow of current in the tube which had been carrying current the unbalance is reversed, that is the action of the two tubes is somewhat analogous to. a snap switch the contacts of which can have only two definite positions and which is so designed that any intermediate positions are unstable and cannot be held for any appreciable time. By applying the phase displaced detector outputs to the two tubes it is possible to cause these detector outputs to throw the unbalance of the tripping circuit back and forth. The output of one detector can be used to cause one tube to take all the current while the output of the second transformer can be used to cause the second tube to-take all the plate current. The phase displaced output from the two detectors will cause first one tube and then the other to carry .plate current but the interval during which one tube carries current will be much greater than the interval available to the other, depending upon whether or not the transmitter whose frequency is being monitored is above or below the frequency of the standard monitoring source. Due to the unbalance in time during which the tubes carry current there will be an unbalance in average dc current which can be utilized to operate the relay RY.

In practice it is very desirable that the tripping circuit be made inoperative unless there is an output from the two detectors and unless the frequency of this output is above a predetermined value. I obtain such an action bynormally biasing the two tripping tubes so highly that no plate current can flow in either of them and then overcome this bias or a portion of it by means of another dc voltage obtained by rectification of a portion of the detector outputs. Thus, I have shown oxide rectifier OR in the sketch to obtain the bucking voltage for the bias source. Since the amplitude of the bucking voltage is proportional to the amplitude of the audio output from the detectors the whole system is relatively insensitive to variations in volume of detector output. This is a desirable feature for practical applications where constant volume would be somewhat difilcult to obtain. In the arrangement which I have shown it is only necessary for the volume to be. sufficiently high to cause the tripping circuit to function. If either the standard frequency'source or the transmitter should fail the tripping tubes are immediately rendered inoperative and no further changes are made in the adjustment of the transmitter frequency control equipment. Consequently, as soon as the failure or interruption of energy is corrected, the transmitter frequency immediately comes again under the control of the correcting device and in no case has been run to the extreme range permitted by the frequency control. Also, if the device is used to monitor the output from a keyed transmitter its operation is not affected by the keying except, of course, that the relay may tend to make contact intermittently if the keying is quite slow.

If desired, the plate currents of the vacuum tubes or vapor devices may, of course, be used to directly operate an alarm device or to control the power supply to a motor without the intermediate control relay. For example, the plate currents of thetwo tubes may be passed through field coils of a small motor in directions to cause opposing fields and in this case the direct resultant fieid magnetization will depend upon the difference between the two tube anode currents.

Further circuits for detecting the phase of the beat by comparing twolike frequencies one of which tends to drift through zero beat, are illustrated in Figures 4 and 5. The circuits of Figures 4 and 5 illustrate means for increasing the speed of detection of the phase shift.

Turning to Figure 4 in greater detail, the input to the tubes I54, I56 corresponding to similarly labeled tubes in Figure 3, is derived from transformers I52, I50 in turn connected to detectors not shown corresponding to the detectors I30, I32 of Figure 3, one of the inputs in either transformer I52 or I50 is leading in phase depending upon whether the frequency to be monitored is above or below the standard frequency from the frequency controlling source. The condenser resistance circuit I and resistors I84, I86 and the feedback through condensers I88, I90 together with the action of transformers I92, I94 all tend to produce an unbalance -in 'plate currents of the two vacuum tubes I54, I56. The current through one or the other tube predominates, of course, when the phase relations of the input from the detector output transformers I50, I52 reverses. The unequal plate currents then cause operation of the electromagnetic relay whose output leads I20 may be connected to any suitable alarm or frequency correcting device such as the frequency correcting motor II4 of Figure 2.

The transformers I92, I94 of Figure 4 are wound upon one core I93 and so arranged that when current through the tube subjected to leading voltages is decreasing, the decreasing current causes an induced E. M. F. in the other coil tending to reduce the plate voltage on the tube experiencing the lagging input voltage. This tends to further rob the lagging tube of current and accentuate the unbalance caused by the phase shift of the beat.

In the phase detector and indicating system of Figure 5 the inputs from two radio frequency detectors such as I30, I32 of Figure 3 are fed into the transformers I50, I52 of Figure 5. As before the condenser-resistance combination I80 is charged first by that tube to which the leading phase currents are applied. The retained charge upon the condenser-resistance combination I80 therefore tends to reduce the current flow through the tube to which the beat is relatively lagging in phase. The transformers I96, I98 are so arranged and connected that as the plate current through that tube to which the leading phase voltages are being appliedidecreases, the induced E. M. F. caused by the decrease in current is such as to reduce the voltage on the grid of the tube being subjected to the lagging beat. In this way the unbalance due to the leading beat is accentuated causing quicker and more positive operation of the alarm or frequency correcting device relay H6, H8. In the arrangement. shown in Figure 5 the grid connections to the transformers I96, I98 may be reversed so that leading voltages applied to one tube in effect causes the other tube to draw current and hence operate the electromagnetic relay H6, H8.

In circuits similar to that shown in Figure 5 I may, of course, use transformer coils I96, I98 to feed back to the screen grid of a four electrode tube instead of to the control grids of three electrode tubes as shown. In fact I may employ tubes with any number of electrodes in any of the cir-' cuits of my invention. I may also use tubes with any type of cathode and, in practice, heater type cathodes, which permit the use of. alternating V 9 heating current without disturbance in the system, are preferred. V

The frequency' controlling systems of Figures 3, 4 and 5 may vary a condenser or an inductor or a combination of both for controlling other 3 forms 'of oscillation generators such as used, for example, in heterodyne receivers or elsewhere.

Also, it is not necessary in connection with long the leads I20 connected to a'reversible motor II4 may supply currents which cause capacity elements 200 to move in opposite directions. The opposite movementis produced by virtue of the internally threaded screw 202 engaging the threaded male supports 204 for the cylindrical sectioned capacity elements 200. The opposite movement is caused by the motor II4 driving the screw 202 through the medium of a suitable screw and gear mechanism 206. Insulating guides line systems that a plate such as II2 of Figure 2 'be moved vertically for, as shown in Figure 8 10 of Figure 6, the pushpull connected vacuum tubes 38, 40 are provided with fluid cooling or water cooling jackets 2I2, 2I4.' The plate or anode circuit of the pushpull connected tubes 38, 40 includes the rectangular or circular flat capacity plates 2I6, 2I8 directly metallically connected to the water cooling jackets 2I2, 2I4. Rotation of knob 220 rotates the screw and gear mechanism 222 and hence the rotation of the internally threaded member 224 in turn causing the variable grounded plates 226 to approach or recede from the condenser plates 2 I6, 2"! simultaneously. As illustrated, condenser plates 226 may be grounded for purposes of symmetry through the gear mechanism and conductor 230.' The inductance of the plate circuit is formed by bi-filarly wound metallic coils 232, 234 to the electrical center 236 of which, bymeans of inlet pipe 238 and outlet pipe 240, cooling fluid or water is introduced or removed from the anode jackets 2 I4, 2I2. For very high frequencies the inductance of the plate circuit may be formed of straight pipes rather than coils. The water cooling system is described in greater detail in United States Patent No. 1,963,131, granted June 19, 1934, to H. E. Hallborg. Anode potential is applied through lead 242 connected to the inlet and outlet pipes 238, 240. If desired 240 may be made the inlet pipe and 238 the outlet pipe, Usually it is best to pass the cooling fluid through the jackets in an upward direction in order to assure that practically all air is forced out of the jacket leaving only the fluid in contact with the anode of the tube. The

' coils 234, 232 which act as'the unitary structure for high frequency electrical currents but has a dual path for cooling fluid, are shown arranged tubes are removed from the jackets. As an aid to prevention of freezing I may use various well known antifreezing mixtures for the cooling liquid.

. For a change in frequency, there are-provided the conductors 244, 246 which are variably tapped to the coils 234, 232, and by connecting the conductors 244, 246 together by means of a suitable switch 248 the effective inductance of the output circuits of the tubes may be varied and hence the frequency may be varied by a relatively large amount, connection of switch 248 to connectors 244, 246 acting to short circuit away a part of the inductance of the plate circuit of the pushpull oscillation generator. Tuning variation may also be accomplished by manipulation of knob 228 hence varyingthe plate tuning condenser 2|6, 226, 2 |8. Output energy is taken by means of coils 258, 252 coupled respectively and inductively to the water cooled coils 234, 232. The coils 258, 252 may lie-connected together and to ground as at 254 and have their other ungrounded terminals connected through by-passing condensers. 256 to a radiating antenna 258. The coils 258, 252 may .be insulatingly supported within and coaxially with the water cooled coils 234, 232, or if desired may be wound about and insulatingly supported from the water cooled coils. If the inductance 232, 234 is formed of straight tubing, as would be the case at very high frequencies then the coupling 258, 252 may also be made of straight conductors placed parallel to and near the conductors 232, 234.

Ii'he grids 268, 262 of the tubes 38, 48 are variably connected through connectors 264, 266 to points 268, 218, on either side of the electrical center 212 of the long line' LLFC for frequency control. Since the system of Figure 6 contemplates very short waves, the long line for frequency control is made in the form of a continuous flattened ellipse with two trough, bent, bottom or 0 portions 214, 216, the midpoints of each trough or. elbow portion 214, 218 being at a voltage nodal point. Intermediate the troughs the portions 218, 288 are linear or straight and are arranged parallel to each other. For frequency adjustment it is preferred that the capacity elements 288 be arranged opposite the midpoint or at a current maximum point on the inner tubular conductor forming part of the long line frequency control system. About the straight portions 218, 288 of the inner tubular conductor of the long line system there are suitably mounted concentric linear tubes or pipes 282, 284 suitably cross-connected and grounded-along their length so as to maintain them at zero radio frequency potential. If desired the outer conductors 282, 284 may be made continuous and completely concentric around the inner conductor 214, 216, 218, 288 but in that case openings for the various connections to the inner transmission line 214, 288, 216, 218 should be provided. The dimensioning of the long line system is preferably made in accordance with that specified for the long line system of Figures 1 and 2 and hence for the sake of brevity will not be repeated here. The overall length of the long line system-shown in Figure 6, that is to saythe mean length of the inner conductor 214, 218, 216, 288, should be a whole number of half wave lengths. long at the desired operating frequency. For adjustment to different frequencies, it should be noted that the same line would be effective for approximately harmonically related frequencies. Hence, by suitably tapping conductors 244, 246 to the water cooled coils, quick change to a harmonically related frequency and stabilization on the same long line may be obtained by the connection of short circuiting strap 248 to the contacts 244, 246. Where operation is desired at frequencies which are not harmonically related I may also provide means for quickly changing the effective length of the line by means of switching in or out sections of line, shunt or series inductance,

capacity, etc. p

- If desired, the long line system may be placed within a suitable container 288 of heat insulating material and the long line system temperature controlled. Moreover, a wall 282 may be placed across one end of the line and temperature controlling fluid fed on one'sideof the wall 282 through tube 284 and removed from the other side of the wall by tube 286, the circulation of fluid through the inner conductor being as indicated by the arrows. Suitable pumping mechanism 288 may be provided for causing a continuous circulation of the temperature controlling fluid in the long line which may be water or oil maintained at asuitable temperature or which maybe air or any gas. In case the circulating fluid or gas is held at a temperature below that of the room or space around the line then some hydroscopic material should be placed ,within the heat insulating material 288 to prevent the formation of water drops upon the long line system. Such condensation, it should be noted, would tend to change the operating frequency due to the fact that it would change the velocity of the electrical waves along the'line.

As a further aid to short wave operation the legs of the filaments of the tubes 38, 48 may be short circuited together for high frequency currents by means of by-passing condensers 388 so that the filament heating conductors 382, 384 act in parallel for high frequency as do also filament heating conductors 386, 388. At the electrical centers 3l8, 3l8, of the loops formed by the heating conductors 382, 384, 386, 388, another by-passing condenser 3l2 may be connected and filament heating energy applied adjacent thereto as for example'by feeding low frequency heating currents thereto by means of a transformer 3. The conductors 382, 384, 386,388 will then act, by judicious choice of their length, as a tuned filament circuit for the high frequency waves and their impedance should be so adjusted as to obtain optimum operating conditions, that is to say, so that the filaments fluctuate at the high frequency potential at a desired amount and wit the desired phase relation.

For modulation any of the schemes described in connection with Figure 2 may be used, it being noted in addition that the source 82 of Figure 2 may be replaced by an amplified alternating current source such as a keyed tone source, or, by

amplified voice currents. Also source 82 may consist of a rectifier supplied with amplified and keyed or modulated relatively low frequency current. For example, in one application of my invention, telegraph signals are sent, from an automatic sender in a central telegraph ofiice, overa wire line, as one channel of a. number of channels carried by the same line, to a radio transmitting station. At the radio station, filters separate the signals of the several channels by frequency discrimination. The energy of one or more channels is then amplified and rectified to supply the input to a transmitter at the point indicated as 82 in Figure 2. As the service requires, the automatic telegraph sender in the central ofiice may be replaced by automatic printer mechanism or by a facsimile transmitter. 1

Another desirable scheme for modulating a. line controlled system is illustrated in Figure 6. Grid bias is fed through conductor 328 to the electrical center 212 of the long line and thence through conductors 264, 266 to the grids 268, 262

of vacuum tubes 38, 48. Variation in the grid bias as impressed by conductor 328 will cause modu-, lation of the output of the frequency controlled system. A pair of diode rectifiers 322, 324 are coupled by means of their plate coil 326 symmetrically to the plate circuit of the pushpull connected tubes 38, 48. By coupling the rectifier coil 326 sufliciently close to the plate circuit, enough of the radio frequency energy developed by the oscillator will be rectified and cause sufficient drop in the resistor R and across radio frequency by-pass condenser C so as to limit the oscillator output.

In addition to this rectifier system for obtaining grid bias there is serially connected a battery 328 which may be replaced by a potentiometer resistor supplied with voltage from a 60 cycle rectifier system. This second source of negative potential 328 serves to adjust the circuitsfor best operating characteristics.

In operation, the two sources of grid bias, namely, source 328 and the bias developed by rectifiers 322, 324 should be adjusted to limit the oscillations developed by the pushpull amplifiers 38, 48 to about half of maximum amplitude. In series with the bias sources there is connected the secondary of a low frequency transformer 338 supplied with amplified tone currents or voice currents from an amplifier 332. The fluctuations in grid bias due to the alternating voltages developed in the secondary of transformer 338 will then vary the output from the oscillator in accordance with modulation.

The advantage of this modulation system resides in the relatively small size of the modulation equipment and also in its relatively small cost.

The plate lead 242 is shown grounded for radio frequency currents by means of a by-passing condenser 334. It may be found desirable in suppressing spurious oscillations not to ground point 236 and in that, event a high frequency choke should be inserted in series with the lead 242 and the end of the choke away from the point 236 should be connected to the by-passing condenser 334.

If desired I may modify the modulating system of Figure 6 by using triode tubes in place ofthe diodes shown at 322 and 324. The triodes will then be suppliedwith direct grid biasing potential either from a. separate source or by means of parallel resistance and capacity connected between the cathodes and ground or source 328.

this drop plus the potential of source 328 when 328 is used, biases tubes 38, 48 to'such an extent and/or frequency multipliers the outputs from which are modulated.

In the long line frequency controlled system of Figure 7, the reversible motor H4 drives a triangular grounded metallic plate 336 back and forth so that the capacity between this plate and the end plates 338, 348 connected to the free electrical ends 342, 344 of the inner transmission line 346, 348, 358 is varied. The outer tubes or pipes 352, 354 are connected together and-grounded as indicated and are used to shield the inner legs 346, 358 of the U-shaped frequency controlling tubular metallic transmisison line. As before the grids of the tubes 38, 48 are connected by means of conductors 264, 266 on opposite sides of the electrical center 212 of the inner concentric conductor. In addition to the neutralizing or feedback control condensers 356, 358, there are provided feedback condensers consisting of inner and outer cylinders 368, 362 and 364 and 366, tube 368 being denser 356, 358 may be had. The plate tuning condenser is diagrammatically shown at 368 con--' nected between the water cooling jackets H2, 2 l4 of vacuum tubes 48, 38. The plate inductance coil in this instance consists of a single doubly Wound metallic tube 318 provided with inlet and outlet water cooling ducts 312. Obviously the plate inductance may be made of straight tubes for very high frequency operation. Output energy may be taken from blocking condensers 315 and fed directly into an antenna or to any subsequent amplifier as found desirable. Plate potential is fed from conductor 242 through two choke .coils 314, 316 to points 318, 388 on opposite sides of the electrical center of the coil 318 which center is preferably madebetween the inlet and out- 382, it is often possible to adjust the circuits to either of two desired operating frequencies much more readily than can be done by varying taps 318, 388 alone. The line for frequency control is well adapted as explained in my above mentioned United States Patent No. 1,945,546, for control at either the fundamental or any harmonic frequency. It should also be noted that, if desired, I may provide more than one frequency controlling line and connect them to the grids of the tubes alternately or in' various combinations to obtain various frequencies and conditions of operation. The changing of connections may be done by manual changing of connections or by means of selective switches as desired. In some cases one operating handle or mechanism will simultaneously operate switch 382 and change frequency controllinglines.

For modulation purposes voice currents from an audio frequency amplifier 384 are impressed upon the transformer 338 corresponding to the transformer 338 of Figure 6. In place of the battery 328 of Figure 6, however, a, rectifier 386 has been illustrated in Figure 7.

The dimensioning of the line system of Figure.

7 should be in accordance with the statements expounded for Figures 1 and 2 and the long line system may be supported if desired as shown in Figures 1a. and lb or may be suspended from an overhead structure such as the ceiling supportin girders of a power house.

It has beenstated that for substantially harmonically related frequencies the same long line .from one to the other. In addition it is preferred that the switching means allow of the use of the same rectifier and modulation supply and apparatus for both long line systems. In this case I may also provide for operating both oscillation systems simultaneously from the same power supply and modulation source. This is desirable at transition periods where one frequency is fad- ,ing out and the other becoming effective,'over a communication circuit, in order that continuous communication may be had while the trafllc is being transferred from one high frequency channel to another.

For temperature compensation of the line system schemes other than the ones suggested may be used, for example, a section of metallic pipe 1 may be run parallel to the line and this pipe may 'be filled with oil or some other liquid having a high temperature coefficient of expansion.. At the end this parallelly run pipe there may be mounted a "sylphon bellows, the end of a which will move back and forth as the temperature of the oil varies. This movement of the bellows may be used to actuate condenser plates for changing the natural period of the line to compensate for changes in temperature, or, it may be used to vary the effective length of the line by moving the telescoped ends of the line. In'connection with this system a crosswise section of piping may be connected to the lengthwise section of the pipe and this cross portion may be mounted within a container about a portion of the frequency controlling line. By varying the length or size of the cross pipe the relative exposure of the whole volume of oil may be controlled in order to obtain proper thermal coupling to room temperature and to the temperature of the inner pipe as a consequence of which the system will compensate for both room temperature variations and temperature rise due to the losses in the lineitself.

It should be understood that the frequency control line of the invention comprises, in efl'ect, a tuned circuit in the form of a resonant line wherer in the inside surfaces of the outer conductors and end boxes form the complete return circuit for currents flowing on the outside surface of the inner conductor. Since the surfaces carrying the high frequency current are of relatively large cross section or circumference and made of relatively low resistance material such as copper,

silver, or gold, there are very low radio frequency losses and as a result the line forms an extremely sharply tuned resonant circuit which can be used to maintain very constant oscillator frequencies.

Although the drawings show the outer conductor of. the frequency control line and the end boxes connected to ground at several points, it is-to be understood that such'ground connections ""fii'e'rely indicate points of zero radio frequency potential, and that it is not necessary to actually ground" the line. As a matter of fact, high frequency circuits seldom, if ever, are designed for actual effective connection to earth. Since the outer surfaces of the whole enclosure for the resonant line, including the outer pipes, end boxes, power amplifier enclosure and supports,

are at zero radio frequency potential, it is common careless practice to speak 'of them as being grounded or at ground potential whereas what is actually meant is that there are no differences in radio frequency potential between any points on their outer surfaces.

Having thus described my invention, what I claim is:

l. A constant frequency oscillation generator comprising a pair of multi-electrode devices each having anode, cathode and grid electrodes, a circuit having inductance and capacity and being approximately resonant to a desired operating frequency connected between said anode electrodes so that said anode electrodes fluctuate in phase opposition, a circuit connected between an intermediate point on said approximately resonant circuit and said cathodes, a U-shaped tube having substantially an electrical overall length of a multiple of one-half wavelength taken at the desired operating frequency, a connection from the trough of said U-shaped tube to said cathode electrodes, and connections from said grid electrodes to points on said U-shaped {tube substantially symmetrically disposed with respect to said aforementioned trough oath e connection.

2. A constant frequency oscillation generator comprising a pair of multi-electrode devices each having anode, cathode and grid electrodes, a circuit having inductance and capacity and being approximately' resonant to a desired operating frequency connected between said anode electrodes so that said anode electrodes fluctuate in phase opposition, a circuit connected between an intermediate point on said approximately resonant circuit and said cathodes, a U-shaped tube having substantially an electrical overall length of one-half wavelength taken at the desired operating frequency, a connection from the trough of'said U-shaped tube to said cathode electrodes, connections from said grid electrodes to points on said U-shaped tube substantially symmetrically disposed with respect to said aforementioned trough-cathode connection, and a grounded metallic cylinder around each leg portion of said U-shaped tube, and insulated therefrom.

I 3. A constant frequency oscillation generator comprising a pair of multi-electrode devices each having anode, cathode and grid electrodes, 2. circuit having inductance and capacity and being approximately resonant to a desired operating frequency connected between said anode electrodes so that said anode electrodes fluctuate in phase opposition, a circuit connected between an intermediate point on said approximately resonant circuit and said cathodes, a U-shaped tube having substantially an overall length of a multiple of one-half wavelength taken at the desired operating frequency, a connection from the trough of said U -shaped tube to said cathode electrodes, connections from said grid electrodes to points on' said U-shaped tube substantially symmetrically disposed with respect to said aforementioned trough cathode connection, a

grounded metallic cylinder about and insulated aooacso 4. A constant frequency oscillation generator comprising a pair of multi-electrode devices each having anode, cathode and grid electrodes, a circuit having inductance and capacity and being approximately resonant to a desired operating frequency connected between said anode electrodes so that said anode electrodes fluctuate in phase opposition, a circuit connected between an intermediate point on said approximately resonant circuit and said cathodes, a U-shaped tube having substantially an overall length of one-half wavelength taken at the desired operating frequency, a connection from the trough of said U-shaped tube to said cathode electrodes, connections from said grid electrodes to points on said U-shaped tube substantially symmetrically disposed with respect to said aforementioned trough cathode connection, a grounded metallic cylinder about and insulated from each leg portion of said U-shaped tube, and means for varying the effective overall electrical length of said U'-shaped tube, said means comprising lengths of tubing telescoped within theopen ends of said 'u-shaped tube.

approximately resonant to a desired operating frequency connected between said anode electrodes so thatsaid anode electrodes fluctuate in phase opposition, a circuit connected between an intermediate point on said approximately resonant circuit and said cathodes, a U-shaped tube having substantially an overall length of onehalf wavelength taken at the desired operating frequency, a connection from the trough of said U-shaped tube to said cathode electrodes, connections from said grid electrodes to points on said U-shaped tube substantially symmetrically disposed with respect to said aforementioned trough cathode connection, a grounded metallic .cylinder about and insulated from each leg porvtion of said -U-shaped tube, means for varying the effective overall .electrical length of said U-shaped tube, and means for varying said last means automatically and in such a way as to cause said multi-electrode devices to generate oscillations'o'f a frequency corresponding to thetrodes, and an accurate frequency controlling circuit coupled to said grid cathode electrodes,

vsaid accurate frequency controlling circuit comprising a pair of linear tubes one within another, each of said tubes being substantially some whole multiple of a quarter wave length long at a desired operating frequency, the ratio of the inside diameter of the outer tube to the outer diam- -eter of the inner tube being not less than 2.5 nor more than 5.0.

7. An oscillation generator comprising a multielectrode device having anode, cathode and grid electrodes, a circuit having inductance and-capacity roughly tuned to a desired frequency of outer tube to the outer diameter of the inner tube being 3.6,said inner tube being substantially onequarter wave length long at a desired operating frequency. v

8. An oscillation generator of. constant frequency comprising apair ofmulti-electrode tubes each having anode, cathode and grid electrodes, a circuit roughly tuned to a desired operating frequency and having inductance and capacity connected between the anode electrodes of said devices so that at the operating frequency the anodes fluctuate out of phase, a circuit connected from an intermediate'point on said roughly tuned circuit to the cathodes of said devices, a U-shaped tube having substantially parallel linear legs, each leg being substantially a quarter wave length long at a desired operating frequency, a connection from the trough portion of said tube to the cathode electrodes of said devices, connections from the grid electrodes of said devices to points on said U-shaped tube on opposite sides of said trough cathode connection, and a grounded metallic linear cylinder disposed about each of the linear legs of said U-shaped tube, the ratio of the inside diameter of each cylinder to the outside diameter of the leg of the U within it being not less than 2.5 nor more than 5.0.

9. An oscillation generator of. constant frequency comprising a pair of multi-electrode tubes each having anode, cathode and grid electrodes, a circuit roughly tuned to a desired operating frequency and having inductanc'e and capacity connected between the anode electrodes of said devices so that at the operating frequency the anodes fluctuate out of phase, a circuit connected from an intermediate point on said roughly tuned circuit to the cathodes of said devices, a U-shaped tube having substantially parallel linear legs, each leg being substantially a quarter wave length cathode electrodes of said devices, connections.

from the grid electrodes of said devices to points on said U-shaped tube on opposite sides of said trough cathode connection, and. a grounded metallic linear cylinder disposed about each of the linear legs of said U-shaped tube, the ratio of the inside diameter of each cylinder to the outside diameter of the leg of the U within it a 50 being 3.6.

10. A system for generating constant frequency oscillations comprising a pair of multi-electrode devices each having anode, cathode and grid electrodes, a circuit having inductance and capacity and roughly tuned to a desired operating frequency connected between said anode electrodes, a circuit connected to an intermediate point on said roughly tuned circuit and to the cathode electrodes of said devices, a flattened metallic tubular ellipse having substantially straight parallel sides and an over-all effective electrical length substantially equal to a multiple of half the length of the fundamental wave, a

, connection from said cathode electrodes to one of the troughs of said ellipse, and connections from said grid electrodes to points symmetrically disposed on said tubular ellipse on opposite sides of said trough cathode connection.

11. Apparatus as claimed in claim 10 characterized by the fact that about each of the straight sides of said tubular ellipse there is insulatingly arranged a grounded metallic cylinder.

12. The method of operating a regenerative oscillation generator so as to reduce loss at high frequencies which includesthe' step of adjusting 

